Impulse modulated magnetron oscillator



,. Aug; 13, 1940, R, BRADEN 2,211,404

IMPULSE M ODULATED MAGNETRON OSCILLATOR l A Filed April 29, 1939 2 Sheets-Sheet l HIGH VOLT/7GB myn p/ wlmi? L'Lzcrno Eene H. Braden Cttorneg Aug. 13,1940. Y R. A. BRADr-:N 2,211,404

IMPULSE MODULATED MAGNETRDN OSCILLATOR Filed April 29. 1939 2 Sheets-Sheet? Fra. f rm* -"1 I I cHHRG/Nl I W/WE 'SHAPE/ I I I I I I J MHG/VE TRON :Inventor H. Braden FWO/1 MopuL/IWA/G W/rvz .sl/HFX Gnome Patented Aug. 13, 1940 PATENT OFFICE IMPULSE MODULATED MAGNETRON OSCILLATOR Rene A. Braden, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 29, 1939, Serial No. 270,831

12 Claims.

netron oscillator.

, responding to the length of an impulse.

The use of ultra high frequency oscillators which are impulse modulated in connection with direction finders and similar devices is well known in the art. Because of its inherent high frequency the magnetron oscillator is particularly adapted to this purpose. It also lends itself to impulse modulation due to its inherent susceptibility to changes in the operating voltages e and the magnetic field. It is, therefore, one of the objects of this invention to provide an improved system for impulse modulating a magnetron oscillator.

The necessity for providing an intense magnetic field increases the weight of the apparatus necessary to produce ultra-high frequency impulses by means of a magnetron oscillator. 'I'his arises from the weight of the magnet core and also from the additional equipment necessary to provide a direct current power supply of suilicient capacity to energize the electromagnet which is commonly utilized. In accordance with this invention, advantage is taken of the fact that in an impulse modulated oscillator energy is supplied only during a brief interval of time. More particularly, the interval during which the oscillator itself does not draw current from the power supply is utilized to store energy for the production of the magnetizing current. Thus, the peak load of the power supply may be reduced, its weight decreased, and the efciency of the system generally improved. It is therefore a further object of this invention to provide a means for alternately applying the energizing potential to the oscillator and to the magnetic system, at the same time taking into consideration the fact that with respect to the oscillator itself the energizing potentials and the magnetizing flux must be present at the same instant.

A further economy is realized by means of the system which has been briefly described above due to the fact that the magnetizing current flows only during a short interval of time cor- This materially reduces the total ,energy necessary since the power consumption in the electromagnet is commonly a large portion of the total power consumed. 'I'hat this is so is evidenced by the fact that a separate power supply system for the electromagnet is usually employed in magnetron oscillators in order to supply suiilcient energy to energize the electromagnet. By means of this invention, therefore, the additional power supply is eliminated since all the magnetizing current is taken from the plate voltage supply during quiescent intervals when the magnetron is in a non-oscillating condition.

This invention will be better understood from the following description when considered in connection with the accompanying drawings, and its scope is indicated by the appended claims.

Referring to the drawings, Figure l illustrates the general arrangement of this invention in i block diagram form; Figure 2 is a chart representing the sequence of events in various units of the system; Figure 3 is a circuit diagram of a device for providing a control voltage of one required wave shape; Figure 4 is a similar del5 vice which may be used to provide a control Voltage of another desired wave shape; and Figure 5 is a schematic diagram of a modulator.

Referring to Fig. 1, a magnetron oscillator is indicated at 'I and consists, for example, of a 20 pair of end plates 9 and II, anode electrodes I3 and I5, and a cathode Il. The anode electrodes I3 and I5 are connected to an antenna I9 by a transmission line 2|, 23 in the well known manner. Anode potential is supplied to the magnetron through a radio frequency choke 25 which is connected between the midpoint of antenna I9 and a voltage regulator and divider 21. Magnetizing flux for the magnetron is supplied by means of an electromagnet comprising a core 29 30 and a winding 3|. The end plates 9 and II are connected to the output of a modulator 33 which will be subsequently described.

While I have illustrated my invention by means of an end plate magnetron, it is to be 35 clearly understood that it is not limited thereto, and may be readily applied to other types of magnetron oscillators which are well known to those skilled in the art. vThe voltage which is applied to the anode electrodes I3' and I5 is 40 adjusted to that value which allows efficient oscillation when the end plate voltage is applied from the modulator 33, and when the magnetic field produced by the electromagnet 29 is at the value which is determined by the control circuit associated therewith. It is Well known that the condition for oscillation is obtained at a critical combination of magnetic flux and electrode potentials, and that the oscillator may be stopped either by increasing or by decreasing the potential applied to the end plate or the anode electrodes, or both. The choice of increasing or decreasing the applied potential requires slight modifications in the arrangement shown, but is undoubtedly well understood by those skilled in theart. -The particular method which I have illustrated is, therefore, to be taken merely by way of illustration and not as a limitation.

Energizing potential for the magnetron electrodes and for the electromagnet is derived from a source oi' direct current potential 35 which may be any suitable system and need not be described in detail. The output is applied to a voltage regulator and divider 21 from which potentials of various magnitudes may be obtained to supply the magnetron and the various units of the system. 'I'he modulator 33 which is included in series with the potential supplied to the end plate electrodes is controlled by a modulating wave shaper 31 the' input to which is derived from an impulse frequency oscillator 39 through a delay network 4|.

In order to provide a magnetizing flux during periods of oscillation, I have provided a capacitor 43 which is adapted to be charged by the high potential source 35 only during the intervals when the oscillator is quiescent. This is accomplished by means of a control tube 45, the anodecathode path of which is serially connected between the potential source 35 and capacitor 43. The grid of the control tube 45 is connected to the output of a charging wave shaper 41 which is connected to the impulse frequency oscillator 39. As a result, during predetermined intervals which are determined by the impulse frequency oscillator 39, the grid of tube 45 becomes positive, permitting a charging current to flow into capacitor 43. Since the impulse frequency oscillator 39 controls both the charging wave shaper 41 and the modulator 33 through the delay network 4|, the necessary time sequence is obtained.

Condenser 43 having been charged, it is now necessary to discharge the condenser through the magnetizing coil 3| at a time which is substantially concurrent with thedesired period of oscillation. Preferably, the discharge should commence before the modulating voltage is applied to the magnetron 1 in order to allow the magnetic ux to build up to a maximum value by the time the modulating impulse arrives. To accomplish this, the energizing coil 3| of the electromagnet is connected between capacitor 43 and the anode of a control tube 49, the cathode of which is connected to ground. 'I'he grid electrode of control pentode 49 is controlled by a voltage which is derived from a magnetizing wave shaper 5| which, in turn, is connected to the impulse frequency oscillator 39.

It is to be noted that the output of the impulse frequency oscillator 39 is connected to a center tapped transformer 53, and that the voltage developed across half of the secondary is applied to the charging wave shaper 41 while the voltage developed across the other half is applied to both the delay network 4| and the magnetizing wave shaper 5|. As a result, during the half cycle whichhas a proper polarity to operate the charging wave shaper 41, the magnetizing wave shaper 5| remains inactive, but it is energized during the other half cycle. Also, it is to be noted that the modulating impulse from 33 is applied to the magnetron during the half cycle of the impulse frequency oscillator which is used to operate the magnetizing wave shaper 5|. Consequently, the positive output impulse from the wave shaper which is applied to the grid of pentode tube 49 permits a substantially constant current to flow through the winding 3| which discharges condenser 63, and produces the desired magnetic field.

The sequence of events and the operation of the device illustrated in Pig. 1 is shown in the curves of Fig. 2, to which reference is now made. Curve c is the sine wave impulse frequency voltage developed across half of the secondary winding of transformer 53 and which is applied to the input o! the charging wave shaper 41. Curve b is a similar voltage of opposite instantaneous polarity which is applied to the input of the delay network4l and the magnetizing wave shaper 5|. Since, as will appear subsequently, the devices 41 and 5| respond to a positive control impulse, it is apparent that they will be made to operate during alternate half cycles of the impulse frequency oscillator.

The output voltage which is obtained from the charging wave shaper 41 is illustrated in curve c. This voltage preferably has the form illustrated, and is substantially constant throughout the first and successive alternate half cycles of the impulse frequency. Since it is only necessary to provide a magnetizing flux during a period which is substantially equal to the impulse period, it is not necessary to pass current through the magnetizing winding 3| during the entire half cycle following the charging of the condenser 43. The magnetizing wave Shaper 5| is therefore designed to produce an output voltage which will control pentode 49 so as to permit the passage of magnetizing current during time periods shown in curve d. The modulating wave Shaper similarly limits the time of the control impulse to a portion of alternate half cycles of the control voltage, and a shortened control voltage is applied by Wave shaper 31 to the modulator 33 so that the end plate voltage is applied to the magnetron during the intervals shown in curve e. It is to be noted that the delay network 4l causes the end plate voltage of curve e to occur ata slightly later instant than the magnetizing current. Since end plate voltage and magnetizing flux occur at the same time, oscillation takes place and the desired impulse is radiated.

An alternative method which eliminates the necessity of providing a delay network as shown at 4| is to so arrange the modulating wave shaper 31 that the modulating impulse is of less duration than the magnetizing impulse. an impulse is illustrated by curve f, and the means for obtaining it will be subsequently described.

Figs. 3 to 5 illustrate wave Shapers and a modulator which may be employed in connection with this invention. The particular systems shown are merely by way of example, and are not, in themselves, a part of this invention. It is well known that there are many methods of limiting the amplitude and duration of a sine wave impulse, any of which are applicable in the present instance.

A preferred arrangement which may be employed to provide a controlimpulse of proper shape to operate tube 45 is illustrated in Fig. 3. The sine wave voltage is applied to a limiting tube 55 through a limiting resistor 51 which is connected in the grid circuit. As is well known, this limits the amplitude of the positive peaks o f the output voltage, While the rectifying action of the tube eliminates the negative half of the control impulse. Tube 59 is a resistance-capacity coupled amplier, the purpose of which is to invert the phase of the output potential of tube 55 so that a positive impulse may Such aan 1,4o4

be obtained from the output terminals. -Ti1e positive impulse is applied between the grid and cathode of tube and permits condenser Il to be charged in the manner which has been described above.

Fig, 4 illustrates a limiter in which the input voltage is applied to a tube 8i through a biasing battery 63. As a result, tube 8| is conductive during only a portion of each successive half cycle since it is operative only in response to a peak voltage greater than the bias provided by battery 63. The impulses are therefore shortened and take the form illustrated in curve d of Fig. 2. In this instance, to illustrate an alternative system, their amplitude is limited by means oi a diode rectifier 85 which is connected across the output load resistor 61 through a biasing battery 69. When the voltage drop across the output load resistor 61 exceeds the voltage oi' the bias battery 69 a low impedance shunt path is provided through tube 65 which effectively prevents a further increase in the output voltage.

'Ihat portion of the device shown in Fig. 4 which is contained within the dotted lines 1| may be used as the modulating wave Shaper 31, since it produces a series of negative impulses which are required to operate the modulator, as will subsequently appear. The magnetizing wave Shaper 5|, however, must deliver positive impulses to the control tube 49, and, as a result, it is necessary to employ a phase inverter tube 13 which is merely a resistance coupled amplifier. The output impulses of short duration are applied to the grid of control tube 49 and permit magnetizing current to flow through coil 3| at the desired instants.

Fig. 5 represents one form of modulator and comprises a modulator tube 15, the grid-cathode potential of which is controlled by the output impulses from the modulating wave shaper 31. Each negative impulse reduces-the anode current of tube 15, reduces the voltage drop across the anode load resistor 11, and causes the potential between ground and its anode to become a maximum. The output voltage of the modulator is applied to the end plates and is sufiicient to cause oscillation during the positive peaks.

'I'he alternative system illustrated in curve ,f of Fig. 2, which was referred to above, eliminates the delay network 4i by reducing the period or length of the control impulse which is applied to the magnetron by the modulator 33. This is accomplished by increasing the bias voltage which ls applied to the control tube 6i so that it operates only on a small peak oi the control potential.

I claim as my invention:

1. In the method of impulse modulating an ultra high frequency oscillator having a plurality of power consuming elements and a source oi power associated therewith, the steps of applying power from said source to at least one of said elements during successive periods separated by alternate intervals, deriving additional power from said source only during said intervals, and applying said derived power to other of said elements during said periods so that the peak load on said source is reduced.

2. The method of impulse modulating an ultra high frequency oscillator including means for producing a magnetic field and a source of energizing current which includes the steps of applying successive modulating potentials derived from said source to said oscillator for discrete periods separated by discrete intervals, de-

riving other energy from said source only during said intervals, storing said derived energy, and

utilizing ,said stored energy to produce said,

magnetic ileld during said discrete periods.

3. The method of impulse modulating an ultra high frequency oscillator including means for producing a magnetic ileld and a source of energizing'current which includes the steps of applying to said oscillator successive pulses of energy derived from said source to cause oscillation for discrete periods separated by discrete intervals, deriving additional energy from said source only during said intervals, and utilizing said derived additional energy to produce said magnetic ileld during said discrete periods.

4. The method of impulse modulating an ultra high frequency oscillator including means for producing a magnetic ileld and a source of energizing current which includes the steps of deriving energy during discrete periods separated by discrete intervals to produce oscillations during said discrete periods, deriving other energy from said source only during said discrete intervals, storing said derived energy, and utilizing said stored energy to produce said magnetic field during said discrete periods.

5. The method of operating an impulse-modulated electron discharge device including a source of energizing current and means for producing a magnetic field which includes the steps of operating said discharge device during discrete periods separated by discrete intervals, charging a capacitor by energy derived from said source during said discrete intervals and utilizing the energy storedv in said capacitor to produce said magnetic ileld during said discrete periods.

6. The method of operating an impulse-modulated electron discharge device including a source of energizing current and means for producing a magnetic field which includes the steps of deriving and storing energy from said source during a first interval, applying energy from said source to said discharge device to produce oscillations during a second interval, and utilizing said stored energy to produce said magnetic field during said second interval to reduce the peak load von said source.

'7. The method of operating an impulse-modulated electron discharge device including a source of energizing current and means for producing a magnetic field which includes the steps of deriving and. storing energy from said source during a first interval, utilizing said stored energy to produce a magnetic field during a second interval, and applying said energy from said source to said discharge device to produce oscillations during a portion of said second interval to reduce the peak load on said source.

8. The method of operating an impulse-modulated electron discharge device including a source of energizing current, an alternating control voltage and means for producing a magnetic eld, which includes the steps of deriving and storing energy from said source during spaced periods which are controlled by alternations of one p0- larity of said alternating control voltage, utilizing said stored energy to produce said magnetic iield during a portion of alternate periods controlled by the alternations of the other polarity of said control voltage, and applying energy from said source to produce oscillations during said portions of said alternate periods.

9. A device of the character described which includes a thermionic discharge device having a plurality of energy consuming elements associated therewith, a source of energy, means for applying said energy to at least one oi' said elements during successive dis'crete periods separated by discrete intervals, means for deriving other energy from said source only duringsaid discrete intervals. and means for applying said other derived energy to other elements during said periods so that the peak load on said source oi power is reduced.

10. The combination which includes a thermionic discharge device, a source of energy. means for producing an alternating controlling potential. means operated by said potential for applying said energy to said discharge device during successive discrete periods separated by discrete intervals, means operated by said potential for deriving additional energy from saidsource only during said discrete intervals, and means for utilizing said derived energy to produce said magneti'c field during said discrete periods.

11. The combination which includes a thermionic discharge device', a source of energy, means for producing an alternating controlling potential, means operated by said potential for applying said energy to said discharge device during successive discrete periods separated by discrete intervals. means operated by said potential ior deriving additional energy from said source only during said discrete intervals, means for storing said derived energy, and means for utilizing said derivedenergy to produce said magnetic ileld during a time at least coextensive with said discrete periods.

l2. The combination which includes a thermionic discharge device having cathode, anode and end plate electrodes, a source of energy, means for applying operating potentials to said electrodes during discrete periods spaced by discrete intervals, a capacitor, means for charging said capacitor from said source oi energy only during said discrete intervals, an electromagnet adapted to pass an axial magnetic ileld through said discharge device, and means for discharging said capacitor through said electromagnet during periods.

RENE A. BRADEN. 

